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Madrepora Classification Essay

Sunrise over the back of NOAA Ship Okeanos Explorer. Click image for credit and larger view.


NOAA Ship Okeanos Explorer
December 21, 2017

Expedition Complete

NOAA Ship Okeanos Explorer pulled into Singing River Island in Pascagoula, Mississippi, first thing this morning. The next couple of days will be very busy as we break things down following 13 active months and get everything ready for the winter in-port before the crew heads home for the holidays.





A red crab sits on a piece of carbonate near a methane seep. The crab is laden with eggs, which are visible on her underside. Click image for credit and larger view.

Deep Discoverer encountered several of these depressions or pockmarks that are likely associated with the release of methane from the seafloor. Click image for credit and larger view.

Deep Discoverer encountered this unusual ctenophore swimming above the seafloor. Click image for credit and larger view.

Watch video of of droplets of methane coming out of the seafloor.


NOAA Ship Okeanos Explorer
December 20, 2017

Dive 17: Horne Dome

Throughout the dive at ‘Horne Dome,’ Deep Discoverer traversed areas of hydrocarbon seepage (discovered at water-column bubble targets) and sedimented seafloor between 1,053 to 1,074 meters (3,455 to 3,524 feet) depth. The site featured four previously undiscovered methane seeps, most of which were were associated with small sedimented mounds suspected to contain methane hydrate. Some of these features also had authigenic carbonate outcrops. Methane-bubble streams were observed at every site, with methane hydrate forming where bubbles were leaving the seafloor or under overhangs. The hydrate was yellow in color, indicating impurities in the gas hydrate or an oily coating on the surface of the hydrate, something that has been seen in other parts of the Gulf of Mexico. We observed ice worms (Hesiocaeca methanicola) in depressions on the hydrates. All of the seeps had small associated chemosynthetic communities, which differed from those observed during other dives on this expedition, being comprised of live and dead vesicomyid clams partially buried within the sediment and many eelpouts resting on the seafloor. Bacterial mats, blackened reduced sediment and tubeworms (Lamellibrachia sp.) with zoanthids growing on the tubes were also common. We observed two kinds of gastropods, Kanoia meroglypta and Phymorhynchus sp., fringing blackened sediment and white bacterial mats. Some of these K. meroglypta hosted juvenile Bathymodiolus mussels, which were also seen on nearby carbonates. One of the chemosynthetic communities was found in a pockmark-like feature, perhaps a collapsed methane-hydrate mound. The last seep had a slightly different faunal assemblage in that it also included adult Bathymodiolus sp. mussels and many chitons (Leptochiton micropustulosus).





Paroriza pallens sea cucumbers were the most frequently encountered large deposit feeders on this dive. The species is hermaphroditic and was often observed in pairs such as this one. The nature of the shaggy filaments hanging from the flanks of these sea cucumbers remains a mystery. Click image for credit and larger view.

A dense cluster of Escarpia sp. chemosynthetic tubeworms at a cold seep, accompanied by an Alvinocaris sp. shrimp and a chaetopterid polychaete waving its pair of feeding palps from its slender bamboo-like tube. Click image for credit and larger view.

Fish experts on the global midwater team were blown away by the appearance of this fish from the genus Leptochilichthys. The observation placed this fish at a shallow depth of 900 meters (2,953 feet), when typical observations place this fish squarely in the bathypelagic zone at ~2,000 meters (6,562 feet). Click image for credit and larger view.

Watch video of a chemosynthetic community.


NOAA Ship Okeanos Explorer
December 19, 2017

Dive 16: Dauphin Dome

During today’s dive, we targeted the western edge of Dauphin Dome that had a number of Bureau of Ocean Energy Management seismic anomalies and water-column bubble targets detected by NOAA Ship Okeanos Explorer. Dauphin Dome featured at least 10 previously undiscovered methane seeps with small associated chemosynthetic communities. Most of these seeps were small crater-like features (the size of Deep Discoverer), lined with authigenic carbonate. Living within most of the seeps were dense bushes of tubeworms (Escarpia sp. and Lamellibrachia sp.), some of which were parasitized by polychaete worms. At the seeps and within these bushes were a variety of organisms, including two species of polychaete worms, squat lobsters, snails, mussels, zoanthids, ophiuroids, actiniarians, hydroids, and large swarms of copepods. At one site, stoloniferan octocorals were also observed growing on the authigenic carbonates. Following the benthic portion of this dive, we conducted four exploratory midwater transects at depths of 900, 700, 500, and 300 meters (2,953, 2,297, 1,640, and 984 feet). A notable sighting of a fish, a look into the trophic ecology of the midwater, a small medusa, and wonderful protists were the biological highlights for this set of midwater transects.





The giant isopod, Bathynomus giganteus, at its burrow tunnel, accompanied by a hitchhiking spider crab, at a depth of 545 meters (1,788 feet). Click image for credit and larger view.

A small shark, perhaps the black dogfish, Centroscyllium fabricii, at a depth of 601 meters (1,972 feet). Click image for credit and larger view.

A siphonophore imaged during one of our midwater transects. Click image for credit and larger view.

Watch video of a swordfish observed feeding.


NOAA Ship Okeanos Explorer
December 18, 2017

Dive 15: Gulfoil

We started today’s dive at “Gulfoil” at a depth of ~615 meters (2,018 feet) on a heavily bioturbated, sedimented seafloor. During the entire dive, only two areas of hard substrate were encountered. Many of the species observed were seen multiple times, indicating an unvarying community. We observed crustaceans, including squat lobsters, crabs, and giant isopods (Bathynomus giganteus) in burrows and depressions, as well as partly buried in the sediment. At least two species of cerianthid anemones were also abundant throughout the dive, and we also saw several deposit-feeding ophiuroids, sea stars, and holothurians. Fish were the second most abundant group of organisms encountered. The two small pieces of hard substrate encountered during the dive were colonized by barnacles (Arcoscalpellum regium) and anemones (Hormathiidae sp.). The lack of hard substrate resulted in actiniarians and zoanthids attaching to other species. Following the benthic portion of the dive, we conducted two exploratory 10-minute midwater transects at 400 and 300 meters (1,312 and 984 feet) depth. While many observations were made during the transects, the constellation fish, Valenciennellus tripunctulatus, was particularly exciting to the team. Characterized by dense marine snow, both midwater transects featured abundant midwater life.





The tripod fish, Bathypterois viridensis, with parasitic isopods attached to two of its fins. Tripod fishes rest on the seafloor on the tips of elongated rays of their pelvic and lower caudal fins. They use the elongated rays of their pectoral fins as sensory “antennae” that project out and forward as the fish sits facing into the current. Click image for credit and larger view.

A coronate medusa, Periphylla periphylla, that collided with the seafloor. These medusae undertake a daily vertical migration (toward the surface at dusk and toward the depths at dawn). It is suspected that this was a reaction to the bright lights on Deep Discoverer; the medusae attempted to swim deeper away from the light they thought was coming from the surface. Click image for credit and larger view.

An olive-colored empty egg case of a cartilaginous fish – either a skate, ray, or shark – attached to the octocoral Swiftia koreni. Click image for credit and larger view.

Watch video of a chimaera seen during the dive.


NOAA Ship Okeanos Explorer
December 17, 2017

Dive 14: “Penchant Basin”

Today’s dive took place at “Penchant Basin,” a geologically active site where possible seeps had been detected via seismic and multibeam surveys. Deep Discoverer touched down at a depth of 800 meters (2,625 feet) on a sedimented seafloor with an abundance of benthopelagic fauna, including many fish species and gelatinous creatures, such as ctenophores, jellies, and siphonophores. Moving upslope, the seafloor was covered with many burrows and mounds, which provided habitat for crustaceans, including blind lobsters (Acanthacaris caeca), giant isopods (Bathynomus giganteus), and galatheid squat lobsters. We also observed small areas of reduced sediments in shallow depressions with bacterial mats, empty vesicomyid (clam) shells, gastropods, tubeworms, and cusk eels. Towards the summit of the slope, we saw two straight-edged elongated carbonate ridges colonized by several coral species, as well as brachiopods, zoanthids, spiny crabs, and encrusting demosponges. One of the most interesting observations for the dive was several elasmobranch (cartilaginous fish) egg cases attached to the octocorals and antipatharians, indicating that these corals are a nursery for elasmobranchsa. Curiously, many of the egg cases had been overgrown by coral tissue with polyps.





A cerianthid burrowing anemone builds a tube in the sediment out of secreted fine threads and mucus, which it can withdraw rapidly into and completely for protection. Click image for credit and larger view.

A cynoglossid tonguefish (Symphurus sp.) related to flounders, soles, and halibut, lies on the sediment. It uses the individual rays of the fins along its sides to creep over the seafloor like a millipede uses its many legs on land. Click image for credit and larger view.

The top of a craggy pinnacle about two meters tall supports a dense community of orange, suspension-feeding, brisingid sea stars and, at the very top, a gorgonocephalid basket star. Click image for credit and larger view.

Watch video of a shortfin squid.


NOAA Ship Okeanos Explorer
December 16, 2017

Dive 13: “Tunica Mound”

Deep Discoverer (D2) touched down on the gently sloping seafloor at “Tunica Mound” at a depth of 395 meters (1,296 feet) and proceeded to climb a series of terraces in the northern section of this area before heading west along a ridge. Most of the area was sedimented and hosted a high diversity of fishes. Invertebrates observed included a variety of crabs, squat lobsters, sea stars, tube-dwelling anemones, and a sea pen with commensal shrimp. Due to the lack of hard substrate, organisms attached where they could; for example, we observed a human-made tube heavily colonized by anemones and hydroids. A number of unknown siboglinid tubeworms with red plumes and Lamellibrachia sp. tubeworms also provided hard substrate for anemones, zoanthids, hydroids and barnacles. As D2 progressed upslope, we observed small carbonate outcrops that harbored a variety of octocorals and black corals. Continuing upslope, we discovered a large craggy rock column about two meters tall of unknown origin and composition covered in brisingid sea stars and surrounded by irregular rubble on the seafloor. Stichopathes sp. antipatharian whips dominated the surrounding rubble but were accompanied by many of the same species observed at previous outcrops. Several species of fishes, including Darwin’s slimehead, conger eels, and a scorpionfish, inhabited nooks in the column. We also saw numerous amphipods on a fragment of water hyacinth and a wood fall surrounded by shrimp and ampharetid polychaete worms, and heavily bored by numerous wood-eating bivalves. Unfortunately, the dive was cut short by deteriorating weather, so we had to recover the remotely operated vehicle early.





After being blown out to sea, this pelican landed on the ship to catch his breath. Click image for credit and larger view.


NOAA Ship Okeanos Explorer
December 15, 2017

Weathered Out (Again)

With the weather taking another turn for the worse, the dive today was canceled. The team on the ship hunkered down, disappointed that the weather was rough and hoping things would settle down so they could dive again.





A hormathiid anemone and hydroids on the underside of the shipping container. Click image for credit and larger view.

The mucous (protein and cellulose) house of a larvacean, a planktonic relative of sea squirts. Although the tadpole-shaped architect that normally resides within may have evacuated (as is normal after a time), the pale central inner filters that it constructs remain visible. The meshes of these filters are so fine that they trap bacteria-sized and smaller particles. Click image for credit and larger view.

A colonial tuscarorid phaeodarean, a relative of radiolarians and foraminiferans, feeding on a filament of marine snow. The individual cells of the colony each secrete a white silica shell, or test, with several fine radiating spines, and together they create the pale sphere composed of fine silica mesh. Seen at a depth of 701 meters (2,300 feet). Click image for credit and larger view.

Watch video of the shipping container.


NOAA Ship Okeanos Explorer
December 14, 2017

Dive 12: “Wreck 15727” and Midwater Exploration

The original purpose of today’s dive was to conduct the first visual survey of a side scan sonar target thought to represent an archaeological site and related debris. However, instead of a shipwreck, we discovered a 40-foot freight-shipping container and its cargo of washing machines, dryers, chest freezers, dishwashers, and refrigerators. After locating identifying markers that may help to track the container, we spent some time documenting the biology on the container and associated debris, observing hydroids and stoloniferan octocorals, as well as a number of fish sheltering in and under the container. We also observed a bamboo coral (Isididae sp.) growing on a washing machine. We made the decision to end the benthic portion of the dive early to conduct transects in the midwater at eight depths from 1,000 meters (3,280 feet) to 300 meters (984 feet), in 100-meter increments. An excellent diversity of midwater animals at temperatures ranging from approximately 4°C (39.2°F) at 1,000 meters to over 13°C (55.4°F) at 300 meters characterized the water column. Animals encountered included ctenophores, siphonophores, medusae, fishes, and shrimp, as well as single-celled and colonial protists. A physonect siphonophore, possibly Apolemia sp., had tentacles emerging from between its nectophores. Several halicreatid medusae were observed along with narcomedusae in the genus Solmissus. A ctenophore in the genus Kiyohimea was found at the end of the 300-meter transect in perhaps the warmest water (over 13.8°C) recorded for this genus. Considering the volume explored and the number of encounters, this midwater environment seemed to be densely populated with a substantial diversity of organisms.





The coiled tip of an isidid bamboo coral whip (Lepidisis caryophyllia) found growing out of a sediment substrate. Click image for credit and larger view.

The anterior end of a chemosynthetic siboglinid tubeworm, Lamellibrachia sp., protrudes from its tube. The red “feathers” are respiratory tentacles filled with hemoglobin-containing “blood.” The white structure is called an obturaculum and functions as a trapdoor that protects the opening when the worm withdraws into its tube. Brown branched hydroid colonies grow on the tube. Click image for credit and larger view.

A sea cucumber (Benthodytes sp. ) and a shrimp (Nematocarcinus sp.) happen to wander near each other. Click image for credit and larger view.

Watch video of an Enypniastes eximia sea cucumber.


NOAA Ship Okeanos Explorer
December 13, 2017

Dive 11: “KC560/603”

Today we explored “KC560,” a young mud volcano. The dive started at a depth of 2,075 meters (1.3 miles), with Deep Discoverer (D2) touching down close to a brine river with blackened reduced sediment, white bacterial mats, and a range of species, including chemosynthetic mussels (Bathymodiolus sp.), tubeworms (Lamellibrachia sp.), filter-feeding polychaete worms, shrimp, squat lobsters, anemones, amphipods, and unknown waving polychaete worms. Growing on authigenic carbonates and asphalt mounds nearby were bushes of Lamellibrachia tubeworms as well as octocorals (Plexauridae sp., Isididae sp., Clavularia rudis) with commensals (brittle stars, crinoids, barnacles, and squat lobsters). Thereafter, geologically active areas were much less common, although some areas that did not appear to be chemosynthetic were inhabited by tubeworms (Siboglinum sp.). Sedimented areas were interspersed with carbonate outcrops that hosted corals and encrusting sponges. Continuing up the sedimented slopes, we observed a high diversity of holothurians and fishes. Moving up the increasingly steeper slope, carbonate outcrops hosted Paramuricea sp. and commensal ophiuroids and squat lobsters. We also saw zoanthids, glass sponges, Chaceon quinquedens red crabs, tube-dwelling anemones, and barnacles. D2 then proceeded to traverse quickly downslope to an unexplored sedimented trough and then up a second local high with more bamboo corals (Lepidisis caryophyllia).





Hariotta raleighana, a long-nosed chimaera, dropped by during the dive. This was the first time many on board has seen one! Click image for credit and larger view.

Bathymodiolus mussel beds are home to a huge variety of invertebrates, including ophiuroids, scaleworms, and limpets. Click image for credit and larger view.

Neolithodes agassizii, a major predator at Gulf of Mexico cold seeps, is observed chowing down on a Bathymodiolus brooksi mussel. Click image for credit and larger view.

Watch video of the brine pool encountered during the dive.


NOAA Ship Okeanos Explorer
December 12, 2017

Dive 10: Green Canyon Area, St. Tammany Basin

During Dive 10, we explored a series of seep targets identified during multibeam surveys by NOAA Ship Okeanos Explorer near a proposed Flower Garden Banks National Marine Sanctuary expansion zone and a proposed Habitat Area of Particular Concern. In the vicinity of the first seep target, we discovered a brine pool fringed by chemosynthetic mussels (Bathymodiolus brooksi). Within the pool, the shells of mussels, that appeared to have drowned when the brine level rose, were visible. Bacterial mats, king crabs, several species of tubeworms, squat lobsters, shrimp, and amphipods were also observed near the brine pool. Nearby, we discovered two additional areas of seepage surrounded by mussel beds and other associated fauna, including one that was quite extensive. The Bathymodiolus mussels varied in size, indicating multiple recruitment events. Under a neighbouring overhang of authigenic carbonate covered with Actinernus anemones, methane hydrate was spotted accumulating. To enable exploration of the second bubble target on the other local high in the area, Deep Discoverer transited quickly over a sedimented plain, where we observed a range of species, including sparse Bathymodiolus brooksi shells, tube-dwelling anemones, several Umbellula sp. sea pens with commensal mysid shrimp, sea cucumbers, and sea urchins. Approaching the second bubble stream, patches of reduced sediments and bacterial mats were seen in increasing frequency. A community of tubeworms, squat lobsters, and shrimp was observed on an outcrop of authigenic carbonate. In this area, Actinernus anemones were also abundant. Throughout the dive, a wide range of fish were observed including two species that had never been seen before!





Two deep-sea male red crabs, Chaceon quinquedens, go claw-to-claw in an apparent duel for the affections of a nearby female. At least, that’s how we interpreted their behavior. Click image for credit and larger view.

Squat lobsters take shelter among a dense cluster of Desmophyllum sp. cup corals and a white Anthothela sp. octocoral growing on the mostly dead skeleton of the stony coral Madrepora oculata. Live colonies of Madrepora oculata can be seen at right and in the background. Click image for credit and larger view.

Watch video of black, viscous bubbles and filaments of tar-like hydrocarbons escape from the seafloor.


NOAA Ship Okeanos Explorer
December 11, 2017

Dive 09: “Henderson Ridge Mid South”

Dive 09 took place on the northern side of a ridge feature at a site dubbed “Henderson Ridge Mid-South,” starting at a depth of 1,260 meters (4,134 feet). During the dive, we explored five possible locations of methane bubble plumes identified during multibeam surveys by NOAA Ship Okeanos Explorer. Progressing through the approximate bubble-stream locations, we observed evidence of chemosynthetic activity at some of the locations, including reduced sediments, bacterial mats, and the shells of dead chemosynthetic mussels. Towards the second half of the dive, incredible deep-sea coral communities appeared, with large colonies of Paramuricea sp., Madrepora oculata, Clavularia rudis, and Enallopsammia sp., many of which hosted diverse communities of commensal invertebrates. Nearly all of the coral communities were confined to asphalt extrusions and carbonate outcrops, indicating how important hard substrates are for increasing the diversity of seafloor communities in predominantly sedimented areas. During the dive, we also observed an area of liquid asphalt seepage with a small community of tubeworms (Lamellibrachia sp.), as well as a previously unknown methane bubble stream that hosted a chemosynthetic community of bacterial mats, mussels (Bathymodiolus spp.), shrimp, eelpout fish, and a variety of other organisms.





A hermit crab (Paguroidea sp.) with an anemone that substitutes for a shell. Click image for credit and larger view.

The chemosynthetic community found at the second bubble target included Lamellibrachia tubeworms, Bathymodiolus mussels, Chiridota holothurians, Alvinocaris shrimp, anemones, and ophiuroids. Click image for credit and larger view.

The ophidiid Penopus microphthalmus imaged at a depth of 2,152 meters (1.34 miles). Click image for credit and larger view.

Watch video of Chiridota sea cucumbers seen during the dive.


NOAA Ship Okeanos Explorer
December 10, 2017

Dive 08: “AT251”

Today’s dive was located in a geologically active area, on a seismic anomaly identified by the Bureau of Ocean Energy Management (BOEM). The dive started on a sedimented slope at 2,160 meters (1.34 miles) depth, with a high diversity of fishes as well as numerous invertebrates, including shrimp, a hermit crab, and brisingid sea stars. Here, we observed a small area of reduced blackened sediment with bacterial mats and chemosynthetic tubeworms and mussels (both dead and alive). As the dive progressed, it became apparent that the feature originally targeted for exploration was covered in a thick layer of sediment and so was unlikely to host the expected coral communities. As a result, the team instead searched for the sources of two bubble plumes detected the previous night during multibeam surveys by NOAA Ship Okeanos Explorer. The first bubble plume could not be located, but tubeworms and bacterial mats were observed at the second bubble target. We also observed numerous burrowing echinoids (Spatangoida) at this reduced area, as well as some small carbonate outcrops that hosted anemones, corallimorphs, and cup corals. Other notable observations included large numbers of sargassum clumps that had drifted down from the sea surface, a small carnivorous sponge (Cladorhizidae sp.), and several pieces of marine debris.





First view of the wreck’s bow outlined by the remnant copper sheathing, with one hawse pipe in foreground and another just aft of the stempost at right. Also visible are white colonies of the stony coral Lophelia pertusa (on the stempost and at far left) and numerous duckbill eels. Click image for credit and larger view.

Transferware teacup and open end of a glass bottle found toward the stern. Click image for credit and larger view.

Ship’s stove, found amidships, is a likely home for two spider crabs, Rochinia crassa. Click image for credit and larger view.

Watch video highlights from the dive.


NOAA Ship Okeanos Explorer
December 9, 2017

Dive 07: Wreck 15377

Dive 07 took place at an unknown shipwreck first identified during an oil and gas industry survey in 2002 and classified by the Bureau of Ocean Energy Management as “ID Number 15377.” During the dive, we conducted a full survey of the wreck, collected imagery to generate a 3D mosaic survey, and documented biology living on the wreck. Deep Discoverer approached the shipwreck from the bow, revealing a wooden hull clad in copper sheets. Lead draft marks tacked to the wreck’s stem post suggest that a large portion of the hull remains buried in the sediment. On the starboard side of the vessel, we documented a large sheet anchor stowed on deck amidships, remnants of a suction bilge pump with cast-iron flywheels, and a ship’s cast-iron stove. Artifacts observed in and around the wreck included a variety of bottles, a basin and pitcher, glassware, and ceramic storage jugs. Based on initial analysis, archaeologists believe the ship likely post-dates 1830 to perhaps mid-century and was likely a merchant vessel, built for distance and capacity over speed. The biology inhabiting the wreck was exciting, including hundreds of “duckbill” Nettastomatidae eels, many spiny crabs (Rochinia crassa), and Chaunax fish. There were also remnants of naval shipworm (possibly Teredo) calcareous burrows in the wooden ribs, likely responsible for the breakdown of much of the structure prior to sinking. Many thick bacterial mats and occasional Lamellibrachia tubeworms indicated the presence of a chemosynthesis-based ecosystem, likely from the degradation of the wood structure.





The calm before the storm: The cold front passes over the ship. Click image for credit and larger view.


NOAA Ship Okeanos Explorer
December 6-8, 2017

Weathered Out

Painfully, every morning for the last three days, we have woken up after mostly sleepless nights to the ship pitching and rolling from the seas and the sound of the wind howling outside our port holes. Early Wednesday, the cold front that brought snow to much of the southeast U.S. passed through the Gulf and brought us 40-knot winds and 14-foot seas for several days. The mission team tried to make the best of the weather days by attempting to collect mapping data when the sea would abate for a few hours as well as catching up on dive summaries and paperwork, but for the most, part we just hunkered down and appreciated the invention of sea sickness medication.





A Metallogorgia sp. octocoral with a commensal serpent star (Ophiocreas sp.). It is suspected that these two species require each others’ presence to survive! Click image for credit and larger view.

A stalked hyocrinid sea lily with Amathillopsis sp. amphipods living on the stalk. These amphipods are usually found in mating pairs and use the stalk’s height off the seafloor to catch particles passing in the water column for food. Click image for credit and larger view.

One of the spectacular sessile communities spotted during the dive. These were mostly comprised of octocorals, black corals, and sponges. Click image for credit and larger view.

Watch video highlights from the dive.


NOAA Ship Okeanos Explorer
December 5, 2017

Dive 06: “Smooth Escarpment Ridge”

Today’s dive was the second of an exploratory pair that compared the geology and associated communities between 1,800-2,300 meters (5,905 - 7,545 feet) depth at the northern end of the West Florida Escarpment. Unlike the first dive, which took place yesterday, this dive explored an area where the escarpment has very reduced promontories, which results in near-vertical slopes. The dive started at a depth of 2,091 meters (6,860 feet) on a sedimented slope with a number of gullies, concretions, and outcrops that provided habitat for numerous fish species, a variety of cnidarian species, and several sponge species. Continuing upslope, the terrain changed to a near-vertical ferromanganese-encrusted cliff wall, which coincided with an increase in abundance and diversity of organisms, including several coral species. In this area, we observed a ledge where the crust acted as a trap for debris, including large ferromanganese-encrusted coral skeletons that had fallen from upslope. As remotely operated vehicle Deep Discoverer ascended the cliff, we observed a number of exposed plateaus with spectacular sessile communities comprised of corals, sponges, and a surprising abundance of crinoids belonging to six or seven different families. Many of the stalked crinoids had commensals, which included featherstars and Amathillopsis sp. amphipods on the stalks. Other notable observations during the dive included an ‘adolescent’ octocoral (Metallogorgia sp.), a dandelion siphonophore, and a number of sea stars consuming octocorals.





Umbellula sea pens are sediment dwellers. This one has a mysid keeping it company. Mysids are commonly known as opossum shrimp, because they have brood pouches. You can catch a glimpse of the full red brood pouch as two red dots on either side of this mysid’s midsection. Click image for credit and larger view.

A polychaete scaleworm (Polynoidae sp.) seen just above the seafloor. The combination of its undulations and the shimmering waves of its oar-like paddles that drive it through the water was positively hypnotic. Click image for credit and larger view.

This cerianthid, a tube-dwelling anemone, is likely an unknown species. This one has built its tube of adhesive threads and sediment in a hole in the carbonate substrate. Click image for credit and larger view.

A hydromedusa observed during midwater transects. Click image for credit and larger view.

Watch video of a glass sponge and its associates.


NOAA Ship Okeanos Explorer
December 4, 2017

Dive 05: “Incised Escarpment Ridge”

Today’s dive was the first of a pair of dives along the northern end of the West Florida Escarpment that compared the geology and associated communities at the two sites. The southern section of the escarpment explored today is marked by promontory features, which have steep slopes that are both sedimented and exposed, resulting in a high species diversity. The dive started at ~2,210 meters (7,250 feet), on a sedimented slope, where Umbellula sp. octocoral, our first for this expedition, was spotted immediately. On this slope, we also observed at least three species of sea cucumbers, shrimp, a xenophyophore, a few fish, and spoon worm feeding tracks. Areas of exposed carbonate rock upslope were colonized by several sponge species, including a number of dead glass sponges with extensive communities of soft coral, barnacles, brittle stars, and amphipods growing on the stalks. We also observed a high diversity of cnidarians on this slope, including at least 12 species of coral. The dive ended in a sedimented area with rock outcrops that hosted sponges, polychaete worms, crinoids, soft corals, octocorals, and bamboo corals.

After leaving the seafloor, we conducted midwater exploratory transects at four depths (900, 700, 500, and 300 meters; 2,953, 2,297, 1,640, and 984 feet). During the midwater survey, we observed a diverse assemblage of organisms, including larvaceans, shrimp, siphonophores, salps, fishes, and several different species of hydromedusae and ctenophores. The greatest diversity and biomass of organisms were observed at 500 meters.





A serpent star, Asteroporpa cf. annulata, clings to the skeleton of bamboo coral. Serpent stars, basket stars, and brittle stars all fall within the class Ophiuroidea. Click image for credit and larger view.

This congrid eel was observed eating a smaller fish. During the dive, we saw nearly 15 different species of fish. Click image for credit and larger view.

Beautiful Gracilechinus gracilis urchins are typically found on hard substrates in the Gulf of Mexico and northwestern Atlantic Ocean. Here you can see the tube feet are extended! Click image for credit and larger view.

Watch video of a searobin seen during the dive.


NOAA Ship Okeanos Explorer
December 3, 2017

Dive 04: “Long Mounds”

Dive 04 took place on the West Florida Escarpment, within a proposed Habitat Area of Particular Concern, beginning at 410 meters (1,345 feet) and ending at 383 meters (1, 256 feet). Given the relatively shallow nature of the dive, we observed life not usually encountered on deeper dives, including a high diversity of fish species. As remotely operated vehicle Deep Discoverer climbed the escarpment and crossed the exposed top edge, fauna transitioned from mostly small encrusting sponges to a diverse suspension-feeding community composed of many bamboo and black corals, and finally to a field of bamboo corals on the shelf top. Notable benthic observations included a congrid eel that captured and ate a smaller fish (Serranidae sp.), a glimpse of a swordfish, a shallow xenophyophore, a young basket star (Gorgonocephalidae sp.), and many live pterobranchs (tiny, colonial, filter-feeding relatives of acorn worms) amongst corals on the upper crest of the escarpment. Most of the science team, both onboard and on shore, had never seen a live pterobranch, so this was particularly exciting! Due to issues with the ship’s dynamic positioning system, a large part of the dive was spent in the water column, where we observed species of coronate jellies, pyrosomes, larvaceans, siphonophores, and ctenophores.





Remotely operated vehicle Deep Discoverer investigates some of the striking geology seen during the dive. Click image for credit and larger view.

A Darwin’s slimehead hangs out a few meters off the bottom. Click image for credit and larger view.

As with our first two dives, Illex sp. shortfin squid were observed during the dive, sometimes in large schools. Click image for credit and larger view.

Watch video of the swimming sea spider.


NOAA Ship Okeanos Explorer
December 2, 2017

Dive 03: “Okeanos Ridge”

Today we explored an area that we have called “Okeanos Ridge,” as it was first mapped by NOAA Ship Okeanos Explorer in 2012. The dive took place within a proposed Habitat Area of Particular Concern, so we were interested in collecting baseline information on the local distribution and abundance of life on the seafloor. We arrived on a sediment-covered canyon floor at a depth of 740 meters (2,428 feet). During the dive, the remotely operated vehicle Deep Discoverer (D2) climbed two areas of an escarpment and crossed the exposed platform between the areas, leading to a variety of benthic habitats. Communities appeared to increase in abundance and diversity as D2 progressed up the escarpment, with the largest coral colonies and greatest abundances of organisms close to the exposed crest; small areas of sediment on the escarpment supported less fauna. As D2 crested the escarpment and followed the exposed edge eastward, we observed a variety of striking carbonate structures, including caves, pillars, and even an “amphitheater,” created when numerous slabs calved off a low wall. Corals observed during the dive included at least five species of black corals; the octocorals Chrysogorgia sp., Acanthogorgia sp., Pseudoanthomastus sp., Plumarella sp., and Isididae sp.; and the stony corals Madrepora oculata, Lophelia pertusa, and Enallopsammia sp. Other organisms included zoanthids, hydroids, featherstars, hexactinellid sponges and purple demosponges. We also observed two mating pairs of golden crabs (Chaceon fenneri), a Gracilechinus urchin and a Circeaster sea star preying on octocorals, and a wood fall (possibly bamboo), which served as habitat for animals such as gastropods and shrimp. Notable water-column observations included two swordfish, a swimming pycnogonid (sea spider), and two cutlass fish (Benthodesmus tenius).





We observed several of these tripod fish (Bathypterois sp.) perched on their fins and facing into the current, waiting for food to drift by. Click image for credit and larger view.

The most dramatic part of the dive was a steep section of wall covered in Euplectellidae sponges. Click image for credit and larger view.

This polychaete worm had incorporated a number of pteropod shells into its tube. Click image for credit and larger view.

Watch video of the "wall of life."


NOAA Ship Okeanos Explorer
December 1, 2017

Dive 02: “Escarpment Canyon”

During Dive 02, we explored a canyon feature along the West Florida Escarpment, southwest of Pulley Ridge, starting at a depth of 2,319 meters (7,608 feet) and working up the canyon wall. The slope of the canyon wall varied throughout the dive, with less steep areas covered in sediment and generally harboring less life than steeper areas with hard, exposed carbonate substrates. Along a particularly steep section of the wall, we encountered an area of exposed hard substrate covered with thousands of glass sponges belonging to the family Euplectellidae. Large coral colonies (Isididae spp., Chrysogorgiidae spp., and Corallium sp.) also appeared in high numbers here, but only on corners and promontories that projected outward from the wall. Many of these coral colonies had commensals such as shrimp, brisingid sea stars, scalpellid barnacles, chirostylid squat lobsters, and featherstars. Other notable observations during the dive included a live larvacean (Bathochordaeus? sp.), an argonaut shell, and a polychaete worm, which had incorporated a number of pteropod shells into its tube. We also collected a bathycrinid sea lily or stalked crinoid that is likely a depth record for its family in the western Atlantic. The geology along the upper edge of the wall was particularly dramatic and consisted of several large, heavily pitted carbonate outcrops. Unfortunately, we encountered a large amount of marine debris throughout the dive, from gaskets and plastic bags to a bucket, glass bottles, and even a fluorescent light bulb.





A chirostylid squat lobster hangs out in an octocoral fan (Paramuricea sp.) that has been overgrown with colonial anemones (zoanthids). Click image for credit and larger view.

Two blind white lobsters (Acanthacaris caeca) share a burrow. Click image for credit and larger view.

Dr. Chuck Messing pulls a carnivorous cladorhizid sponge sample out of Deep Discoverer’s biobox. Click image for credit and larger view.

Watch video of the giant isopod seen during the dive.


NOAA Ship Okeanos Explorer
November 30, 2017

Dive 01: “South Reed”

Today’s dive took place at “South Reed,” a site southwest of Florida located in an area proposed as a Habitat Area of Particular Concern by the Gulf of Mexico Fishery Management Council. The remotely operated vehicle (ROV) Deep Discoverer touched down at a depth of 816 meters (2,677 feet) on a fine muddy bottom and immediately encountered large numbers of shortfin squid (Illex sp.). We saw these squid throughout the dive. Their aggregation may have been associated with breeding, because we saw many dead specimens; squid often die after reproducing. We also saw the giant deep-sea isopod pill bug, Bathynomus giganteus, as well as several species of decapod crustaceans, including Chaceon fenneri (golden crab), C. quinquedens (red crab), royal red shrimp (Pleoticus robustus), and Nematocarcinus sp. shrimp. These decapods highlight the importance of the area, as all are commercially fished species. Some of the most extraordinary organisms encountered were several species of sponge in the family Cladorhizidae – extraordinary because, unlike all other sponges, which feed on extremely small suspended particles, members of this family are carnivorous and trap small crustaceans on their hook-like skeletal spicules. Moving up the first escarpment, we encountered several species of bryozoans (moss animals), octocorals, and black corals with zoanthids and sponges. Many of them harbored commensals, including squat lobsters, shrimps, and scale worms. Continuing up slope, coral rubble appeared in increasing abundance and transitioned into an area of lightly sedimented hard substrate with patches of dead colonies of the branching stony coral, Lophelia pertusa. On the second escarpment, the bottom community became more diverse and dense, and included the stony corals Lophelia pertusa, Madrepora occulata, and solitary cup corals, as well as the octocorals Acanthogorgia sp., Paramuricea sp., and Pseudoanthomastus sp. Many of these also hosted commensals. The geology along the upper edge of the second escarpment was particularly dramatic, consisting of several small walls of limestone. The dive ended at the local high of the escarpment (645 meters; 2,116 feet), a flat terrace dominated by a high density of three species of black corals (Antipatharia).





A dolphin rides the bow as the ship leaves port. Click image for credit and larger view.


NOAA Ship Okeanos Explorer
November 29, 2017


On a beautiful Key West morning, NOAA Ship Okeanos Explorer got underway and commenced mapping towards our first dive site. During our departure, we had the good luck to have a couple of dolphins escort us out of the harbor, which is traditional a good luck sign to mariners. Throughout the day, the science team spent the day familiarizing themselves with the ship and the remotely operated vehicle team made their final preparations for the expedition. We are all very much looking forward to our first dive tomorrow.






















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In this article we will discuss about Coelenterata:- 1. History of Coelenterata 2. General Characters of Coelenterata 3. Classification 4. Tissues 5. Polyp and Medusa 6. Polymorphism 7. Corals.


  1. History of Coelenterata
  2. General Characters of Coelenterata
  3. Classification of Coelenterata
  4. Tissues of Coelenterata
  5. Polyp and Medusa of Coelenterata
  6. Polymorphism of Coelenterata
  7. Corals of Coelenterata

1. History of Coelentrata:

Aristotle knew the stinging qualities of coelenterates and considered these organisms as intermediate between plants and animals and termed them Acalephae or Cnidae (Gr., akalephe = nettle; cnidos = thread). They were long included in the Zoophyta (Gr., zoon = animal; phyton = plant) together with various forms from sponges to ascidians.

The animal nature of coelenterates was established by Peyssonel (1723) and Trembley (1744). Linnaeus, Lamarck and Cuvier grouped the coelenterates under Radiata which included the echinoderms also because of their symmetry. Finally, Leuckart (1847) separated the coelenterates from echinoderms and created a separate phylum Coelenterata (Gr., koilos = cavity; enteron – intestine).

However, the Coelenterata of Leuckart also included the sponges and ctenophores.

Hatschek (1888) splitted Leuckart’s Coelenterata into three distinct phyla – Spongiaria (Porifera), Cnidaria (Coelenterata) and Ctenophora.

The coelenterates or cnidaria are distinguished from sponges in being “tissue animals” (Metazoa) that have distinct digestive cavity. The coelenterates differ from ctenophores in being primarily radial in symmetry, in possessing nematocysts, in having a polyp stage, and in reproducing both asexually and sexually.

Coelenterata or Cnidaria are radially symmetrical diploblastic animals with only epidermis and gastrodermis, between these two layers is a jelly-like mesogloea which is originally structure less but in higher forms, it becomes fibrous and has wandering amoebocytes.

Epidermis and gastrodermis are in two layers, each made of a variety of cells showing a division of labour, the cells form poorly organised body tissues. All functions of the body are performed by tissues and never by organs.

The radially symmetrical body has an oral-aboral axis, there is a single coelenteron or gastro vascular cavity which has only one aperture, the mouth. The mouth is used both for ingestion and egestion. There is no coelom. They bear tentacles and nematocysts. The nervous system is a primitive nerve net. They may have an exoskeleton, and in some there is an endoskeleton.

There is an oval ciliated planula larva during development. Coelenterata include some 9,000 living species and there are many known fossil forms dating back to the Ordovician period. Except for a few species of freshwater forms almost all Coelenterata are marine. They include hydras, jelly-fishes, sea anemones, and corals. The phylum is divided into three classes, namely, Hydrozoa, Scyphozoa and Anthozoa.

2. General Characters of Coelenterata:

1. Coelenterates are Metazoa or multicellular animals with tissue grade of organisation.

2. They are aquatic, mostly marine except few freshwater forms like Hydra.

3. They are sedentary or free-swimming and solitary or colonial.

4. Individuals are radially or bi-radially symmetrical with a central gastro vascular cavity communicating to the exterior by the mouth.

5. They are diploblastic animals; body wall consists of an outer layer of cells called ectoderm and inner layer of cells the endoderm cemented together by an intermediate layer of non-cellular gelatinous mesogloea.

6. Acoelomate animals because they do not possess a second body cavity, the coelom.

7. Short and slender tentacles encircle the mouth in one or more whorls.

8. The tentacles are provided with nematocysts; tentacles serve for food capture, its ingestion and for defence. These are also present on body layers, these are adhesive organs.

9. They exhibit the phenomenon of polymorphism with very few exceptions; the main types of zooids in polymorphic forms are polyps and medusa. Polyp is sessile and asexual zooid, while medusa is free-swimming and sexual zooid.

10. Skeleton, either exoskeleton or endoskeleton is of common occurrence.

11. They are usually carnivorous; digestion is extracellular as well as intracellular. Anus is not found.

12. Nervous system consists of one or more networks or nerve-cells and neurites located in the ectoderm and endoderm.

13. Respiratory, circulatory and excretory systems are wanting.

14. Reproduction is both by asexual and sexual methods.

15. Asexual reproduction occurs by budding and sexual reproduction by the formation of gametes.

16. A ciliated planula larva usually present in the life history.

17. The life history exhibits the phenomena of alternation of generations or metagenesis in which the asexual polypoid, sessile generation alternates with sexual medusoid, free-swimming generations.

3. Classification of Coelenterata:

The classification followed here is given by Hyman, L.H,. (1940). According to Hyman, Phylum Coelenterata has been divided into three classes, viz., Hydrozoa, Scyphozoa and Anthozoa.

Class I. Hydrozoa:

(Gr., hydra = water; zoios = animal):

1. Hydrozoa are solitary and freshwater or mostly colonial and marine, sessile and free- swimming forms.

2. They exhibit tetramerous or polymerous radial symmetry.

3. Body wall consists of an outer ectoderm and an inner endoderm separated by non- cellular mesogloea.

4. Gastrovascular cavity without stomodae­um, septa or nematocysts bearing gastric filament.

5. Skeleton or horny structure is horny peri- sarc in some forms, while coenosarc sec­retes a skeleton of calcium carbonate forming massive stony structure or coral in other forms.

6. They exhibit polymorphism, There are two main types of zooids, the polyp and medusa.

7. Medusa is provided with true muscular velum.

8. Many Hydrozoa exhibit alternation of generations.

9. Reproductive products or sex cells are usually ectodermal in origin and discharged externally.

10. Cleavage is holoblastic, embryo ciliated planula.

Order 1. Hydroida:

1. Solitary or colonial forms.

2. Polypoid generation well developed gives rise to free or abortive medusae by budding.

3. Sense organs of medusae are ocelli and statocysts and exclusively ectodermal in origin.

Suborder 1. Anthomedusae or Athecata:

1. Solitary or colonial.

2. Polyps are not enclosed in hydrothecae and the medusae are also naked without gonothecae.

3. Medusae are tall, bell-like, bearing gonads on the manubrium having strongly arched umbrella.

4. Medusae bear eye spots or ocelli at the bases of tentacles.

5. Statocysts are absent.


Hydra, Tubularia, Bougainvil- lea, Hydractinia, Eudendrium, Pennaria.

Suborder 2. Leptomedusae or Thecata:

1. Colonial Hydrozoa.

2. Polyps are enclosed in hydrotheca and medusae are covered with gonothecae.

3. Free medusae are flattened, bowl or saucer- shaped, bearing gonads on the radial canals.

4. Medusae usually bear statocysts.

5. Eye spots or ocelli are absent


Obelia, Sertularia, Plumularia, Campanularia.

Order 2. Milleporina:

1. Colonial coral-like Hydrozoa without perisarc.

2. Massive calcareous skeleton is secreted by ectoderm provided with pores through which polyps protrude out.

3. Colony have two kinds of zooids, the gastrozooid and the dactylozooid.

4. Gastrozooids (nutritive zooids) are short provided with mouth and tentacles.

5. Dactylozooids are elongate, hollow, slender with tentacles but without mouth.

6. Medusae develop in small chambers, becoming free, devoid of mouth, radial canals and tentacles.



Order 3. Stylasterina:

1. Colonial coral-like Hydrozoa colony have two kinds of zooids, the dactylozooids and gastrozooids.

2. Dactylozooids are small, solid without tentacles.

3. Gastrozooids have a cup with pointed spine.

4. Medusae develop in special cavities redu­ced to sporosacs.

5. Larva is liberated as planula.



Order 4. Trachylina:

1. Polypoid stage reduced or absent.

2. Medusae are large, provided with tentaculocysts, statocysts and lithocysts enclosed in the endoderm.

Suborder 1. Trachymedusae:

1. Margin of the umbrella is smooth.

2. Manubrium is long.

3. Gonads borne on the radial canals.



Suborder 2. Narcomedusae:

1. Margin of the umbrella is scalloped or clefted by tentacle bases.

2. Manubrium is short.

3. Gonads borne in the floor of the stomach.


Cunina, Solmaris.

Order 5. Siphonophora:

1. Siphonophora are polymorphic, free swim­ming or floating colonial Hydrozoa.

2. Colony consists of several types of polypoid and medusoid individuals attached to stem or disc.

3. Polyps without tentacles.

4. Medusae always incomplete and rarely freed.

Suborder 1. Calycophora:

1. The upper end of the colony is provided with one or more swimming bells.

2. Apical float or pneumatophore absent.



Suborder 2. Physophorida:

1. Upper end of the colony bears a float or pneumatophore.


Physalia, Velella, Porpita, Halistemma.

Class II. Scyphozoa (Gr., skyphos = cup; zoios = animal):

1. Scyphozoa include large jelly-fishes or true medusae are exclusively marine.

2. Medusae are large, bell or umbrella-shaped, without true velum, free swimming or attached by an aboral stalk.

3. Marginal sense organs are tentaculocysts having endodermal statoliths.

4. Polypoid generation absent or represented by small polyp, the scyphistoma which gives rise to medusae by strobilisation or transverse fission.

5. Gastrovascular system without stomo­daeum with gastric filaments and may or may not be divided into four inter-radial pockets by septa.

6. Mesogloea is usually cellular.

7. Gonads are endodermal and the sex cells are discharged.

Order 1. Stauromedusae or Lucernaridae:

1. Sessile, sedentary Scyphozoa attached by an aboral stalk.

2. Body globet or trumpet shaped.

3. Mouth cruciform (four cornered) with small oral lobes and a short quadrangular manubrium.

4. Gastrovascular system is divided into central stomach and four per-radial pouches by the four inter-radial septa.

5. Gonads are elongated band-like borne on the faces of septa.

6. Marginal sense organs absent.

7. Fertilisation is external.

8. Larva is planula without cilia.


Lucernaria, Haliclystus.

Order 2. Cubomedusae or Carybdeida:

1. Free-swimming Scyphozoa found in warm and shallow waters of tropical and subtropical regions.

2. Body cubical with four flat sides.

3. Four hollow inter-radial tentacles borne on the margin of the sub-umbrella.

4. Four per-radial tentaculocysts or rhopalia are present.

5. Each tentaculocyst is provided with a lithocyst and one or more ocelli.

6. Mouth is cruciform and gastric pouches are present.

7. Gonads are leaf-like.


Charybdaea, Tamoya.

Order 3. Coronate:

1. Free-swimming scyphomedusae found inhabiting the deep waters of ocean.

2. Body conical, dome-shaped or flattened, grooved.

3. The umbrella is divided by a coronal groove (horizontal furrow) into an upper cone and a lower crown.

4. The crown consists of pedal lobes, pedalia.

5. The pedalia bear solid tentacles.

6. The bell margin is scalloped into lappets alternate with pedalia.

7. Mouth is cruciform.

8. Tentaculocysts are four to sixteen.


Pericolpa, Periphylla.

Order 4. Semaeostomeae:

1. Most common free-swimming medusae found inhabiting the coastal waters of all oceans.

2. The umbrella is flat, saucer or bowl-shaped.

3. Mouth is square.

4. The corners of the mouth produce four oral arms which are grooved with frilled edges.

5. The margin of the umbrella is fringed with hollow tentacles.

6. Eight or more tentaculocysts are present.

7. Gastric pouches and filaments are absent.


Aurelia, Cynaea.

Order 5. Rbizostomae:

1. Free-swimming Scyphozoa found in shallow waters of tropical and subtropical oceans.

2. The umbrella is saucer or bowl-shaped or flattened or even concave on the top.

3. Mouth is surrounded by eight oral arms, bearing numerous funnel-shaped mouth on their edges.

4. Marginal tentacles are absent but 8 or more tentaculocysts are present.

5. Four sub-genital pits are generally present.


Rhizostoma or Pilema, Cassiopeia.

Class III. Anthozoa: (Gr., anthos = flower; zoios = animal):

1. Solitary or colonial exclusively marine forms.

2. They are exclusively polypoid.

3. Medusoid stage is altogether absent.

4. Body usually cylindrical with hexamerous, octomerous or polymerous biradial or radio bilateral symmetry.

5. The oral end of the body is expanded radially into an oral disc bearing hollow tentacles surrounding the mouth in the centre.

6. The stomodaeum is present, often provided with one or more ciliated grooves the siphonoglyphs.

7. Gastro vascular cavity is divided into compartments by complete or incomplete septa or mesenteries.

8. Mesenteries bear nematocysts at their inner free edges.

9. Mesogloea contains fibrous connective tissue and amoeboid cells.

10. Skeleton either external or internal.

11. Exoskeleton is formed from calcium carbonate which often form massive corals.

12. Nervous system is in the form of typical nerve net without a concentrated central nervous system.

13. Gonads are endodermal, develop in the mesenteries.

14. The ripe sexual products are discharged into coelenteron.

15. Fertilisation is external.

16. The fertilised egg develops into a planula larva, which after a short free life settles down and develops into an adult.

Subclass 1. Alcyonaria or Octocorallia:

1. Colonial marine forms.

2. Polyps are long or short cylinder terminating orally into a flat circular oral disc having the oval or elongated mouth in the centre.

3. Polyps always bear eight pinnate, hollow tentacles.

4. Eight complete mesenteries are present.

5. Single ventral siphonoglyph is present.

6. Endoskeleton is the product of mesogleal cells comprised calcareous spicules either calcareous or horny in nature.

7. Polyps are dimorphic in some forms.

Order 1. Stolonifera:

1. The Stolonifera are inhabitants of shallow waters in the tropical and temperate regions.

2. Polyps arise singly from a creeping base and are connected by one or more solenial tubes.

3. Skeleton consists of loose spicules or of compact tubes and platforms.


Tubipora, Clavuldria.

Order 2. Telestacea:

1. Colony consists of simple or branched stems arising from a creeping base.

2. Each stem is very elongated polyp bearing lateral polyps.

3. Skeleton consists of spicules fused by calcareous or horny secretions.



Order 3. Alcyonacea:

1. Colony mushroom-shaped or branched into stout blunt processes.

2. Lower part of the polyp fused into a fleshy mass with only oral ends protruding.

3. Polyps are dimorphic in some forms bearing autozooids and siphonozooids.

4. Skeleton consists of separate calcareous spicules, not axial.


Alcyonium, Xenia.

Order 4. Coenothecalia:

1. Skeleton is massive, composed of crystalline calcareous fibres of calcium carbonate, not of fused spicules.

2. Skeleton is perforated by numerous larger and smaller erect cavities. The larger ones contain the lower ends of the polyps, while the smaller ones the erect terminal tubes.

3. Commonly known as blue corals found on the coral reefs in the Indo-Pacific.



Order 5. Gorgonacea:

1. The colony is usually plant-like, consists of a main stem arising from basal plate or tuft of stolon’s and number of branches bearing polyps.

2. The axial skeleton composed of calcareous spicules or horn-like material, gorgonin is present.

3. Commonly known as sea fans, sea feathers and sea whips are found in tropical and subtropical shores.


Gorgonia, Corallium.

Order 6. Pennatulacea:

1. The colony is elongated and divided into a proximal stalk or peduncle and a distal rachis.

2. Peduncle is embedded in the mud and sand.

3. Rachis is the axial polyp bears numerous dimorphic polyps on its lateral branches.

4. The main stem is supported by calcareous or horny skeleton.


Pennatula, Renilla, Cavernu- laria, Pteroides.

Subclass II. Zoantharia or Hexacorallia:

1. Solitary or colonial marine forms.

2. Tentacles simple, rarely branched hollow cone-shaped, numerous arranged in the multiple of five and six but never eight.

3. Mesenteries are numerous arranged in the multiple of five or six, may be complete or incomplete.

4. Two siphonoglyphs are commonly present.

5. Endoskeleton when present is calcareous, derived from ectoderm.

6. Polyps are usually monomorphic.

Order 1. Actiniaria:

1. Solitary or colonial.

2. Body cylindrical divided into oral disc, column and base.

3. The aboral end is also provided with a pedal disc.

4. Tentacles and mesenteries are numerous and often arranged in the multiple of six.

5. Siphonoglyph is one or more.

6. Skeleton absent.


Actinia, Metridium, Adamsia, Edwardsia.

Order 2. Madreporaria:

1. Mostly colonial rarely solitary form.

2. Exoskeleton is hard and calcareous secreted by the ectoderm.

3. Polyps are small enclosed in the cup-like cavities of the exoskeleton.

4. Siphonoglyph is usually absent.


Astraea, Fungia, Favia, Madrepora, Meandrina.

Order 3. Zoanthidea:

1. Mostly colonial some times solitary forms.

2. Skeleton and pedal disc absent, but the body wall may contain calcareous bodies.

3. Polyps are generally small.

4. Mesenteries are paired. A pair composed of one complete and one incomplete mesentery.

5. Only one ventral siphonoglyph present.



Order 4. Antipatharia:

1. Plant-like colonial forms found in the deep waters in the oceans.

2. The lower end of the colony usually consists of a basal plate for the attachment with some objects.

3. Skeleton in the form of a branched chitinoid axis derived from the ectoderm.

4. The axial skeleton bears the polyps which are dioecious but the colony may be hermaphrodite.

5. Mesenteries and tentacles are 6-24 in number.

6. Two siphonoglyphs present.



Order 5. Ceriantharia:

1. Long solitary anemone-like forms living in the vertical cylindrical cavities in the sea bottom.

2. Body smooth cylindrical and elongated with an oral disc.

3. Pedal disc and skeleton absent.

4. Tentacles are simple numerous and of two types, marginal and oral.

5. Mesenteries are numerous, single and complete.

6. Only single dorsal siphonoglyph present.



4. Tissues of Coelenterata:

The tissues of Coelenterata consist of ectoderm and endoderm, each forming a single layer of a variety of cells, and Coelenterata are regarded as animals at the tissue level of organisation. Together the cells form a thin body wall surrounding an enteron cavity. Increase in thickness and complexity of the body wall is made possible by the development of an intermediate gelatinous layer called mesogloea.

The polyps of lower Coelenterata have a very thin mesogloea, but in polyps of Anthozoa the mesogloea contains fibres and cells and it has become much thicker; in the larger medusae it is very thick and firm, it has become like an internal skeleton and it also stores food.

The chief type of cell found in lower Coelenterata is a columnar epitheliomuscular cell produced into muscle fibres which are embedded in the mesogloea. Such a cell is like a protozoan because its parts carry on different functions.

The endodermal cells can form flagella for churning up the fluid in the enteron, or the flagella can be withdrawn and pseudopodia formed by the same cells for engulfing food into food vacuoles, the same cells also form muscle processes for contraction.

Thus, all the functions of the body are carried out by tissues and never by organs though specialised structures, such as tentaculocysts, may be regarded as organs, but in general the Coelenterata have reached only a tissue-grade of organisation.

5. Polyp and Medusa of Coelenterata:

The polyp leads an easy sedentary life, it has a fixed cylindrical body with a comparatively thin body wall, the free distal end has a hypostome with an apical mouth leading into an enteron, below the hypostome is a circle of extensible tentacles directed upwards and armed with nematocysts, the tentacles may be hollow containing an extension of the enteron, the proximal end of the polyp is closed.

The medusa leads a freely drifting life which requires an elaborate structure and physiological development. Great widening of the body has occurred, especially along the oral surface. The enteron is restricted to a central gastric cavity and canals, this is due to an increase in thickness of the mesogloea on the aboral side which pushes the two endoderm layers together to form a double layered endoderm lamella.

The hypostome has become the manubrium whose rim has become wide and bent downward to form a bell, this has pushed the tentacles to the margin of the bell, tentacles hang downwards, and at times a second set of tentacles may develop on the manubrium.

The muscular system of the medusa is highly developed because the muscular portion of epitheliomuscular cells increases to form elongated striated muscle fibres and the epithelial part diminishes. The nervous system is diffuse, as in the polyp, but in some medusae it becomes concentrated to form a nerve ring and in connection with this well defined sense organs are formed.

6. Polymorphism of Coelenterata:

Polymorphism (Gr., poly = many; morphe = form) is the occurrence of several different types of individuals or zooids in a single species during its life cycle or as members of the colony, the members perform different functions so that there is a division of labour amongst the members.

Coelenterata are noted for their polymorphism, but the various types are reducible to either a polypoid or medusoid type. The polyp and medusa occur in a number of morphological variations. However, polymorphism may be defined as the representation of a single organism by more than one kind of individuals or zooids which differ in their form and function.

Patterns of Polymorphism:

Most Hydrozoa exhibit dimorphism, there is a nutritive polyp or gastrozooid which is sessile, it has a mouth, tentacles and an enteron cavity for food.

The second individual is a medusa which is jelly-like, saucer-shaped, with tentacles on the margin, it is free-swimming and bears gonads. Alcyonaria have only polyps, but they are dimorphic, a nutritive and reproductive polyp called autozooid which has tentacles, gonads and mesenteries; the other polyp is a siphonozooid with no tentacles or gonads, it only maintains a circulation of water in the canals of the colony.

Some hydrozoan colonies are trimorphic, besides the nutritive polyps and reproductive medusae, they also have modified polyps called gonozooids or blastostyles, often enclosed in a chitinous gonotheca, they have no mouth or tentacles, and they produce medusae or their morphological equivalents by budding.

Siphonophora show the highest degree of polymorphism which is not found anywhere else in the animal kingdom. They may have three kinds of polypoid zooids and four kinds of medusoid zooids.

The Polypoid Zooids are as follows:

1. Gastrozooids are tubular or saccular with a mouth, and there may be one tentacle bearing nematocysts. They are used for digestion and ingestion of liquid food. Usually a single long and contractile hollow tentacle arises from the base of gastrozooid which bears numerous fine lateral contractile branches called tentilla. The tentilla has knob or coil of nematocysts.

2. Dactylozooids are for defence and obtaining food, they are tubular with no mouth, with a long tentacle armed with batteries of nematocysts. Modified dactylozooids associated with gonophores on gonozooids are termed gonopalpons. The dactylozooids are also called palpons or feelers.

3. Gonozooids may be like gastrozooids or they may be branching blastostyles bearing clusters of degenerate male and female medusae which produce germ cells for reproduction. Mostly, the gonozooids take the form of a branched stalk called gonodendron having tufts of gonophores with gonopalpons.

The Medusoid Zooids are as follows:

1. Pneumatophore is a gas-filled vesicle or bladder which functions as a float and helps in swimming, the pneumatophore is an inverted medusoid devoid of mesogloea, but its walls are muscular and it has gas glands. It shows great variation in its structure and size in different siphonophores.

2. Phyllozooids are leaf-like bracts or thick and gelatinous medusoids having a canal of the enteron. They are protective and shield some zooids of a colony.

3. Nectocalyces or nectophores are bell-shaped medusoids with a velum, radial canals and circular canal, they have no mouth, manubrium, tentacles or sense organs, A nectocalyx is muscular and brings about locomotion of the colony by swimming. It is also referred to as nectophore or nectozooid.

4. Gonophores occur singly or in clusters on blastostyles, they are degenerate medusae with no mouth, tentacles or sense organs, but they have a velum, canals and a manubrium which bears gonads. Gonophores are dioecious and produce germ cells for reproduction.

Origin of Polymorphism:

A number of theories are given to illustrate the origin of polymorphism in Coelenterata; some of these theories are as follows:

1. Poly-organ Theory:

This theory was proposed by Huxley, Eschscholtz and Metschnikoff.

According to this theory, a polymorphic colony is supposed to be a single medusoid zooid; its various components are regarded to be the modified organs of this medusoid zooid. The various parts of the zooid, i.e., manubrium, tentacles, umbrella, etc., multiply independently from one another and they have assumed different forms to perform different functions.

2. Poly-person Theory:

This theory was proposed by Leuckart, Vogt and Gegenbaur. According to this theory, a polymorphic coelenterate is supposed to be a colonial form in which various types of zooids have been aggregated to perform different functions. All the zooids of the colony are either polyps or medusae or both but the primitive zooid of the colony is of polyp type.

3. Haeckel, Balfour and Sedgwick have agreed that poly-person theory is more correct but they are of the view that the primitive zooid of the colony is probably medusoid which have produced other medusae by asexual budding. Thus, the zooids of the colony are nothing more than the organs of medusiform zooid which have shifted their attachment.

4. Recently, Moser has revived the poly-organ theory. According to him, the various zooids of the colony are organs which have not yet attained the grade of polymorphic form. Thus, the siphonophores are the most primitive existing coelenterates. This theory has not been recognised in general because it altogether denies the colonial nature of siphonophores.

Polymorphism and Alternation of Generations:

Polymorphism is, no doubt, a phenomenon of division of labour, i.e., different functions are attributed to different individuals of the polymorphic form, rather than to the parts or organs of one individual or zooid. All the members of the colony whether polypoids or medusoids, are formed from the coenosarc. Polymorphism is associated with the life cycles of Coelenterata.

In monomorphic forms, like Hydra, the polyp reproduces both asexually and sexually, this condition also applies to Anthozoa. The life cycle remains very simple; it may be represented as polyp-egg-polyp. With the origin of polymorphism, the reproductive powers of the organisms are divided among the different zooids of the colony.

In these cases the polyps reproduce asexually to give rise to medusoid forms (i.e., gonophores) which reproduce sexually to form polyp. The life cycle, thus, becomes complicated and may be represented as polyp-medusa-egg-planulapolyp. Therefore, the so called alternation of generations or metagenesis comes into existence where, in fact, asexual polypoid generation alternates sexual medusoid generation.

Significance of Polymorphism:

The polymorphism is essentially a phenomenon of division of labour in which different functions are performed by the different members or zooids of the colony, viz., polyps are related to feeding and asexual reproduction, while medusae are related to sexual reproduction and so on.

7. Corals of Coelenterata:

Corals are animals belonging to the phylum Coelenterata. These are solitary or colonial polypoid forms and live in a skeleton of calcium carbonate secreted by themselves. Some of them grow into huge mounds, while others are large and branched colonies. However, most of the corals belong to the class Anthozoa and few others to the class Hydrozoa.

The hydrozoan corals belong to order Milleporina, e.g., Millepora and order Stylasterina, e.g., Stylaster. These are colonial forms and secrete massive exoskeletons. Within the exoskeletons, two types of polypoid forms, the gastrozooids and branched dactylozooids are found.

In fact, the epidermis of these polypoid forms is modified and referred to as the calicoblast layer which secretes the calcareous exoskeleton. These corals are found with other corals forming huge mounds.

The anthozoan corals belong to subclasses Octocorallia and Hexacorallia both. The Octocorallia corals belong to order Stolonifera, e.g., Tubipora; order Alcyonacea, e.g., Alcyonium; order Coenothecalia, e.g., Heliopora and order Gorgonacea including sea fans like Gorgonia and Corallium.

The Hexacorallia corals belong to the order Madreporaria, e.g., Astraea, Fungia, Madrepora and Meandrina, etc.; and to the order Antipatharia, e.g., Antipathes.

Among Octocorallia, Stolonifera includes colonial corals like Tubipora or organ pipe coral. In it, the skeleton is made of fused calcareous spicules which form vertical parallel tubes connected together by platforms. The skeleton is tinged red by iron salts and the polyps lie in the tubes partly projecting above.

It is widely distributed on coral reefs. The Alcyonacea includes soft corals like Alcyonium. In it the coral is a colony of polyps having an endoskeleton of separate caleareous spicules embedded in its massive mesogloea.

The Coenothecalia includes a single genus of blue coral, the Heliopora. In it the coral is a colony of polyps which secrete calcareous spicules to form a massive skeleton called corallium. The Gorgonacea includes horny corals, the sea fans like Gorgonia. In it the coral is a branched colony of polyps which secrete a horny proteinaceous material with calcareous spicules around the polyps.

Among Hexacorallia, Antipatharia includes black corals like Antipathes. In it the colony is tree-like and its skeleton consists of branched chitinoid axis. The Madreporaria includes stony corals or true corals like mushroom coral (Fungia), star coral (Astraea) and brain coral (Meandrina or Meandra). Among these some are solitary, while most of them are colonial forms and the principal builders of the coral reefs.

The stony corals, in general, have polyps which are very similar in structure to sea anemones with tentacles and mesenteries in multiples of six, but they are different in having no siphonoglyphs and in being usually colonial. They have an ectodermal external skeleton of calcium carbonate. The exoskeleton of a polyp is called a corallite, and the exoskeleton of the colony is a corallum.

The epidermis of polyp secretes a basal disc of calcium carbonate, then walls of a cup called theca which immovably encloses the polyp, in the theca are radiating septa like mesenteries of an anemone, the septa bear nematocyst. In the centre of the theca is a vertical rod called columella to which the primary septa are fused.

All these form the exoskeleton of a polyp, the polyp fills the corallite and partly projects above. In a colony thousands of polyp form their corallites which are fused together to form a corallum, but all the polyps in a corallum are joined together by lateral connections. A coral colony increases in size by budding new polyps along the margin of the colony. Feeding in corals occurs only at night.

The corals, in general, have diverse shapes and sizes, some are solitary and have large polyps, but the majority are colonial with very small polyps. Some corals are used as ornaments and jewellery. Coral colonies are most abundant in tropical seas though some occur in arctic and temperate seas, but most of them flourish at a temperature above 22°C.

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